Fourteen Chinese and sixteen Causasian normal volunteers were administered a single dose of desipramine. Plasma and urine samples were analysed for DMI and an active metabolite, hydroxydesipramine. To date it appears that the proportion of Chinese that are slow hydroxylators of desipramine is larger than for Caucasians. This may be the reason for tricylic antidepressant dosing of Chinese at lower rates compared with Caucasians. In addition, the renal clearance of hydroxydesipramine was lower in older subjects.